FIG. 1 illustrates a constitution of a general thermal fuse. In thermal fuse 1, lead wires 21 and 22 are connected to case 10 made of a conductive metal, and insulating material 30, springs 41 and 42, movable electrode 50 and fuse element 60 are installed inside the case 10. The spring 41 is disposed between the movable electrode 50 and the insulating material 30, and the spring 42 is disposed between the movable electrode 50 and the fuse element 60. The movable electrode 50 is movable while contacting with the inner surface of the case 10. At normal time (the state of FIG. 1), the thermal fuse is energized from the lead wire 21 to the movable electrode 50 and the case 10, further to the lead wire 22. Then, when the thermal fuse is overheated due to an excess load on the connected electronic device or the like, the fuse element 60 is deformed and melted at a predetermined operating temperature (generally around 240° C.). Thus, the spring 42 is elongated due to unloading, and at the same time, the spring 41 is elongated, whereby the movable electrode 50 moves apart from the lead wire 21. The electric current is cut off by the above operation.
The constituent material of the movable electrode of the thermal fuse having the above operative mechanism is required to have welding resistance on the lead wire and the inner surface of the case, in addition to the conductivity as the electrode material. This is because, the movable electrode is energized in contact with the lead wire constantly, and when welding is generated, it becomes a factor of the operational failure of the thermal fuse. To this request, an Ag—CuO-based oxide-dispersed alloy is known as the constituent material of a conventional movable electrode (Patent Literature 1: hereinafter, this Ag—CuO-based oxide-dispersed alloy is referred to as an Ag—CuO-based alloy).
The Ag—CuO-based alloy is an alloy in which CuO is dispersed in Ag as a matrix, and is excellent in welding resistance and also excellent in high conductivity and stable low contact resistance characteristics, thus has characteristics most required for a movable electrode. Moreover, the application example of the Ag—CuO-based alloy increases also because it does not use Cd that is a harmful substance different from an Ag—CdO-based alloy used before then.